Fatigue crack growth and crack closure behavior of the CrNiMo steels at negative stress ratio

Fatigue crack growth rates and crack closure behavior of three CrNiMo high strength steels were examined at four different stress ratios ranging from R=–1.0 to R=0.5, with attention focussed on the crack closure behavior when R<0. In the latter circumstances, crack closure is lower, and a higher crack growth rate, da/dn, is observed, due to increased compressive deformation, and correspondingly less residual displacement, on crack surfaces. Fatigue crack growth rates measured at different stress ratios could be normalized in terms of the effective stress intensity range, ΔKeff, in which the fracture was formed principlly by quasi-cleavage and dimpled rupture mechanisms.